1. Field of the Invention
The present invention relates to fire emergency signaling systems, and more particularly, to a visual signaling system detectable by hearing impaired persons by providing a strobe light output that can be varied in intensity depending on a desired application.
2. Description of Related Art
Building fire warning systems are required by law and now commonplace in most commercial structures. These warning systems generally include an audible signaling device, such as a horn, siren or bell, that provides an audible signal at a decibel level sufficiently high to be heard by persons within a limited vicinity of the warning system. Audible signaling systems have a significant disadvantage in that they cannot be detected by persons that have impaired hearing. To address this serious deficiency, the fire safety industry introduced signaling devices which included a flashing strobe light in addition to the audible systems. In 1990, the Americans with Disabilities Act (ADA) recognized the importance of such visual signaling devices for assuring access to public facilities to persons with physical disabilities. The ADA specifically included provisions and standards for visual and audible signaling devices designed for the protection of the hearing impaired. Similarly, other industry-based regulatory bodies, such as the National Fire Protection Association (NFPA), Underwriter's Laboratories (UL), the American National Standards Institute (ANSI), and the National Electrical Manufacturers Association (NEMA), have also moved to require such visual signaling devices.
There are four general requirements of visual signaling devices, including intensity, flash rate, placement, and light distribution. Compliance with these four requirements is complicated, however, since the governmental and industry-based standards set forth inconsistent requirements for light intensity. Under the ADA, the visual signaling devices must provide a minimum light intensity of 75 candela (cd) in all areas and that the devices be spaced so that no place in any room is more than 50 feet from the nearest device. In contrast, the industry-based standards recognize that an equivalent illuminance to 75 cd can be achieved using lower intensity strobes (e.g.,15 or 30 cd) spaced closer together (e.g., within 20 feet). The industry-based standards also differ from the ADA in that they set forth different intensity requirements for sleeping and non-sleeping areas. Sleeping areas are given a much higher intensity requirement than non-sleeping areas so that the visual signaling devices will wake hearing impaired persons from their sleep.
The requirements for flash rate, light distribution, and placement also differ in certain respects. The ADA and other standards each require a flash rate from 1 to 3 Hz. Since some individuals are vulnerable to photosensitive epilepsy, it is undesirable to have multiple flashing strobes within an individual's field of view. To address this problem, the National Fire Alarm Code issued by the NFPA requires that the visual signaling devices flash in synchronization, while the ADA does not require synchronized flashing. Similarly, with respect to light distribution, the industry-based standards each require "polar" light distribution, while the ADA does not include any requirement for light distribution. Polar light distribution refers to the way the light intensity is measured in the horizontal and vertical directions at viewing angles ranging between 0 and 180 degrees. Lastly, the placement requirement of the ADA and other standards differs in that the ADA requires the visual signaling devices to be placed on the wall only, while the other standards permit wall or ceiling placement. It should be appreciated that the particular placement will affect the equivalent illuminance provided by the visual signaling devices, as discussed above.
There is a movement within the industry to standardize the various conflicting requirements of the ADA and industry-based standards. In the meantime, however, it is very difficult to provide a single visual signaling system that complies with all of the foregoing requirements. Accordingly, it would be very desirable to provide a visual signaling system that can be adapted for operation under any of the prevailing standards. Such a system would ideally comply with whatever requirements that are ultimately adopted as the various conflicting standards are eventually standardized.